Method of making spring cords



Jan 12, 1950 E. c. HARDSTY ETAL 2,920,351

METHOD OF MAKING SPRING CORDS Filed Aug. 29. 1957 Ffa 6 A a /l/ENTORS E. C. HARDESTY D. L. MYERS BVYQ.Q.

A TTORNEY United States Patent Gliiee 2,920,351 METHOD F MAKING SPRING CORDS Edwin C. Hardesty and Daryl L. Myers, Baltimore, Md., assignors to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Application August 29, A1957, Serial No. 681,035

4 claims. (ci. 1st-56) This invention relates to a method of making spring cords, and more particularly spring cords of helically coiled form.

In the telephone teld and the eld of Various electrical appliances, it sometimes occurs that, because of the length of the electrical cord utilized, kinking and twisting will 'occur in the cord during use. In order to overcome such a kinking and twisting, it has been the practice in certain applications to utilize spring or retractile cords which are -formed normally in a compact helical coil, and which will lengthen during tension but will return to the normal coiled position upon the removal of tension therefrom.

There have been various ways of forming spring cords in the past which are generally satisfactory. However, it

Uhas been found that in instances in the manufacture thereof in the past, the iinal product is not even throughout in that the individual convolutions may be of varying diameter, the pitch of individual convolutions may differ with `respect to the pitch of other convolutions, and the convolutions are not spaced evenly. While this is not a serious defect, it does result in a spring cord which does not throughout.

It has been the usual practice in the past in the manufacture of spring cords to rst wind a section of cordage on a mandrel, at the same time placing an axial twist in the cordage. Further, in many instances prior to the placing of the tinal insulating jacket thereon, the individual insulated conductors may be twisted with respect to each other. While such operations have produced a generally satisfactory cord, it requires added manufacturing operations to impart the axial twist to the final jacketed conductor or to twist the individual insulated conductors which ultimately are jacketed.

It is an object of the present invention to produce an improved spring cord wherein no twist is imparted to the individual conductors or thejacketed cord prior to or at the time of helically coiling the same.

It is a further object of the invention to produce a spring cord wherein the convolutions are of equal size and compact throughout.

It is va still further object of the invention to produce a spring cord wherein the convolutions are formed of equal pitch. It is yet another object of the invention to produce a spring cord wherein no twist is impartedV to the individual conductors or the inal insulated product prior to the reversal thereof.

It is still another object of the invention to produce a spring cord wherein the forces necessary for retractability are enhanced during a reversal of the pitch of the convolutions of the cord.

A further object of the invention is to produce a spring cord wherein no axial twist is placed in either the ndividual conductors or the iinal product prior to the reversal of the helical convolutions of the cord, at which time an added twist is given thereto to impart additional appear to be even and compact to assure that the convolutions therein are compact and of equal pitch and diameter.

An understanding of the invention may be had by the following detailed description thereof when reviewed in conjunction with the accompanying drawing, wherein:

Fig. l illustrates a cord after it is Wound initially on a mandrel in a helical coil;

Fig. 2 illustrates an oven in which the helically wound cord of Fig. 1 is subjected to heat treatment;

Fig. 3 illustrates the cord after heat treatment and removal from the mandrel;

p Fig 4 illustrates a spring cord after reversal of the helices of the coil, as it is made currently;

Fig. 5 illustrates a spring cord after reversal and with overtwist imparted thereto, and

Fig. 6 illustrates the spring cord of Fig. 5 with the overtwist substantially all removed.

Generally, one type of the improved spring cord consists of a plurality of insulated conductors having an insulating jacket thereover which is wound in helical form on a mandrel but to which is imparted no axial twist, after which it is heat treated on the mandrel in an oven to impart a set thereto. The spring cord is then removed flom the mandrel, and the helices of the cord are reversed to impart an opposite pitch thereto and to introduce retractile forces within the cord, but during the reversal coiling operation the convolutions are overtwisted to an extent greater than necessary to form the coils to impart additional forces therein, and thereafter substantially all of the overtwist is removed or unwound from the helically coiled cord.

A method of forming the type of cord referred to above may include the steps of winding a conducting cord, consisting of a plurality of insulated conductors having an insulating jacket thereon, in a helical shape on a mandrel but to none of which is imparted an axial twist, and thereafter heat treating the cord to set the helical shape therein. After heat treating and cooling, the cord may be removed from the mandrel and the pitch of the convolutions reversed to form a helical coil and to introduce retractile forces therein. During reversal, an overtwist is imparted to the coils, that is, the cord is twisted to an amount greater than necessary to form a series of coils therein to impart additional forces thereto. After overtwisting, substantially all of the overtwist is removed, thereby resulting in a finished' product having even-sized convolutions of equal pitch and compact with respect to each other.

With reference to Fig. 1, there is illustrated an nsulated conducting cord 11 which has been wound on ka mandrel, indicated generally by the numeral 12, with the opposite ends of the cord 11 being secured to the mandrel. Such a type of mandrel may consist of a center rod on which is provided a pair of adjustable stops, one of which is usually stationary to permit the mandrel to be inserted in the machine with which it is used. The stationary stop is provided with a suitable catch to secure the forward end of the spring cord thereto. After the cord is wound on the mandrel, the ksecond stop is secured to the rod adjacent to the terminal convolution. The second stop is also provided with a catch to secure the trailing end of the cord. A mandrel of this general type is disclosed more in detail in Patent 2,565,465, issued on August 28, 1951, to W. L. Ames.

The terminal portions of the cord 11 have not been illustrated in Fig. 1, but it should be understood that they may be plain severed ends or they may be tipped and banded, as shown in Fig. 3.

In forming the cord in the helical coil on the mandrel 12, it has been the usual practice to secure the forward end of the cord 11 to the catch on the stationary stop forces Within the cord and then to rotate the mandrel 12 while. moving it longiabove.

i 17 is further provided with bands 20 near tudinally with respect to the supply of cord. It has also been the general practice to rotate the supply of cord on an axis perpendicular to the line of advance of the cord toward the mandrel -to impart an axial twist theretorwhich sets up torsional strains in therco'rd.' After the, complete .helical coil is formed, the second stop is positioned and the trailing portion of the cord secured, as described The individual conductors may or may not have been axially twisted prior to the coiling and axial twisting of the jacketed conductor 11. Y Y

One method of and apparatus for winding the cord 11 on the mandrel 12 with an axial twist thereto is disclosed in Patent 2,413,715, issued to A. R. Kemp et al. on January 7, 1947. f f' As may be seen-in Fig. l, the cord 11, after theinitial winding on the mandrel 12, consists of a helical coil with the individual convolutions having the same pitch,

approximately theY same Ydiavmeter,v and being compact Y.

with respect to each other. v

In performing the method to produce an improved cord under the instant invention, it is contemplated that the jacketed cord, such as 11, will-be coiled on a mandrel, such as 12, in a manner similar to that disclosed above, with the exception that no axial twist will be imparted either to the jack'eted cord or to the vindividual insulated conductors therein. Thus, the cord may be connected to the stationary stop on the mandrel, and theV mandrel then may be rotated and moved longitudinally with respect to the supply of cord to form helical convolutions in the cord about the mandrel, but with no axial y,twist therein. After a sufficient `amount of cord is'wound ron the mandrel, the movable mandrel stopvwill bepositoned -adjacent to the terminal convolution ofthe cord, and the trailing end of the cord'secured therein. 'At this time no retractile forces are yet imparted to the cord.v

After the conducting cord 11 is formed on the mandrel 12, it is placed on a rack 13 which, when filled, is placed within a heat treat oven 14. The oven may be heated by any suitable and conventional means, such as electrical coils 16. The cord 11 within the oven 14` will be heated toa suitable'temperature for a suitabletime in order that the cloiling strains in the insulation are relieved to the amount that thev insulation takes on a permanent set and retains its helical shape. Y x

Afaer the cord 11 is properly heat treated, it is re-Y moved from the oven 14 and permitted to cool suii- Vciently to a temperature at which it may be handled. Fig. 3 illustrates a partially finished springcord, de'sig- Ynated generally by the numeral 17, which has beenY removed from the mandrel 12 after heat treatment. It may be noted that the cord 17 is formed with individual -insulated conductors 18 which have electrical connect- `ing -tips 19 secured to the extremity thereof. The cord thefextremities thereof to secure the insulated jacket-at a point near which it ends and from which the conductors 1S extend.

After the spring cord 17 is removed from the mandrel 12, the pitch of the convolutions of the cord is reversed, such as illustrated by a spring rcord indicated generally by the numeral 21 in Fig. 4'. `Such a reversal of the pitch of the convolutions may be done in various ways. One method of reversal of pitch is to engage one'end of the heat treated helical coil and to draw it lthrough the coil helix, which results in a cord having the pitch ofthe lhelices reversed. This method is illustrated in Patent No. 2,271,057, issued to W. T. Barrans on January 27, 1942.

It should be noted [that the reversal of the, pitch of the convolutions of the coil introduces forces within the cord which enhance retractibih'ty. f

By reference to Fig. 4, it maybe seen, however, that the pitch of thepconvolutions of the cord 21 are not all the same, and that there is varying` distance between adjacent convolutions of the cord. Further, because ofthe dierence in pitch in the individual convolutions 'of the cord, as such convolutions are compacted with respect t0 y of conductors'therein.

4. i each other, there will be evident a dilference in the diameter of the individual convolutions.

ln order to provide a spring cord which doesnot possess the varying pitch, spacing and diameter of the individual convolutions, as disclosed in Fig. 4, it is proposed during the reversing ofthe pitch of the helices of the coil to overwind or overtwist the helicalcoil to an extent greater than is necessary to form the reversed pitch convolutions therein; that is','to impart a greater number of turns or twists than necessary. As a'result of the overtwisting of the spring cord, thev convolutions at that time will be greater in number, will bevery compact and will assume a smaller diameter than the nished product, such as shown in an unfinished spring cord indicated generally by the numeral 22 in Fig. 5.

As the result of the imparting of overtwist in the cord, there will be introduced the additional strains which are `necessary to equalize the forces introducedrin the cord which enhance the retractability of the cord; that is, the overtwist will provide the necessary additional equalizin'g strains within the cord itself so that, when the cord is repeatedly extended,V it will automatically return to its initial compact form with equal diameter and equal pitch convolutions after the release of tension thereon; Y

After the cord has been overtwisted to a desired extent, such as is illustrated by spring cord 22 in Fig. 5, opposite twist yor uncoiling will be imparted-thereto to permit substantially all of the overtwist to be removed from the cord.

A cord with rsubstantially all of the overtwist removed is-illustrated by a spring cord designated generally by the numeral 23 in Fig. 6. It may be noted by examining this illustration that the pitch of individual convolutions is theV same, that the convolutions are compact with respect to each other, and that the diameter of all vof the convolutions is substantially the same. Further,

there is a less number of convolutions in the cord 23 than lin the cord 22 of Fig. 5.

It is understood vthat in the making of spring cords, during the reversal operation to provide a cord such-as illustrated in Fig. 4, a certain amount of force is developed in the insulating covering on the cord which may be, for example, polyvinyl chloride. However, the forces `imparted to the insulation may not always be equal Vspacing of the throughout, resulting in the Variedpitch, diameter and individual convolutions which occur. 'It has been found that by overtwisting the cord during its manufacture, such as illustrated in Fig. 5, and'then by removing substantially all of the overtwist to obtain a finished cord, such as is illustrated as cord 23 in'Fig. 6, that the forces in the insulation are evenedeoutoverthe entire surface of the cord, therebyV achieving the' equal pitch, diameter and spacing of the cord, as illustrated by spring cord 23 in Fig.r 6.

Apparatus for reversing the convolutions of the spring cord, overtwisting the spring cord, andthen removing substantially all of the overtwist is disclosed in copending application Serial No. 681,034,-filed on August 29, 1957, in the name of E. L. Franke, Jr., and assigned to applicants assignee. As disclosed in j-the last-mentioned application, it is desirable to extend or, tension the spring cord during the reverse coiling `and.'oyertwisting thereofto prevent knotting of the spring cord. ,l

Inthe making of spring cords for the telephone eld, wherein the telephone receiver is connected byda spring cord Vto the telephoneset, it is commonrpractice toutilize cords of various lengths and havinga dilferent number For example, th'epspring'cord may be made having 3, v4, 5 lor 6 separate insulated conductors therein over which there is a 'commoninsulating jacket. Likewise, the 'spring cords are usually made in lengths of4 l`ef`:t,'51/2` feet,9 feetor 13 feet. Y i 'In viewof'jthe varied lengths'and number of con- 'ductorsf withinthe jacket, the amount of overtwist and removal of overtwistV will depend on the'particular type of spring cord which is being made at any one time. In order to determine the proper amount of overtwist and removal of overtwist, it will be necessary, depending on the type of machine utilized for performing those operations, to adjust it to give the proper number of overtwists and twist removals to provide a cord of maximum etciency and utility.

Although a speciiic embodiment of the invention has been illustrated and described, it will be understood that this embodiment is but illustrative, and that various modifications may be made therein without departing from the scope and spirit of this invention.

What is claimed is:

l. In the method of making a spring cord which includes the steps of forming a straight length of a cord having an elastic jacket into a helical form, heat treating the thus-formed cord to set the cord in said helical form and then completely reversing the direction of the convolutions of the helically formed cord to enhance the retractibility thereof, the provement which comprises applying tension to the cord to hold the cord extended, and twisting the reversed cord to impart additional convolutions of the reversed direction thereto so that all of the convolutions are reduced in diameter and strains induced in the various components of the cord during the formation and reversal thereof are distributed substantially uniformly throughout the cord, whereby the convolutions remaining in the cord, when the cord is unrestrained, are of substantially uniform pitch, diameter and spacing.

2. In the method of making a spring cord which includes the steps of forming a straight length of a cord having an elastic jacket into a helical form, heat treating the thus-formed cord to set the cord in said helical form and then completely reversing the direction of the convolutions of the helically formed cord to enhance the retractibility thereof, the improvement which comprises applying tension to the cord to hold the cord extended, and twisting the reversed cord in a direction such as to impart additional convolutions ofthe reversed direction thereto so that all of the convolutions are reduced in diameter and strains induced in the various components of the cord during the formation and reversal thereof are distributed substantially uniformly throughout the cord, and then untwisting the cord by an amount suflicient to remove said additional convolutions, whereby the convolutions remaining in the cord when the cord is unrestrained are of substantially uniform pitch, diameter and spacing.

3. In the method of making a spring cord which includes the steps of forming a straight length of a cord having an elastic jacket into a tight helical form on a mandrel of a predetermined uniform diameter, heat treating the thus-formed cord to set the cord in said helical form, removing the helically formed cord from the mandrel and subsequently completely reversing the direction of the convolutions of the helically formed cord to enhance the retractibility thereof, the improvement which comprises applying longitudinal tic jacket and set in a helicallyI coiled form, which method comprises extending the coiled cord longitudinally, gripping the opposite ends of the coiled cord, twistingly rotating one end relative to the other on its own axis and in the same direction as the pitch of the helix while maintaining the coiled cord extended until the direction of all of the coils is reversed and the cord is recoiled in the opposite helical direction, and continuing the rotating step until additional convolutions of the reverse direction are imparted to the recoiled cord so that all of the convolutions are reduced in diameter and strains induced in the various components of the cord during the formation and reversal thereof are distributed substantially uniformly throughout the cord, whereby the convolutions remaining in the cord when the cord is unrestrained are of substantially unifom pitch, diameter and spacing.

References Cited in the le of this patent UNITED STATES PATENTS 

